1. Field of the Invention
The present invention relates to an arteriosclerosis evaluating apparatus for evaluating a degree of arteriosclerosis of a living subject, based on pulse-wave-propagation-velocity-related information (e.g., a pulse-wave propagation time or a pulse-wave propagation velocity) that is related to a velocity at which a pulse wave propagates in the subject.
2. Related Art Statement
Arteriosclerosis is known as a factor that influences pulse-wave-propagation-velocity-related information. This is utilized to evaluate a degree of arteriosclerosis of a living subject based on pulse-wave-propagation-velocity-related information obtained from the subject. For example, an apparatus disclosed in Japanese patent document No. 9-122091 or its corresponding U.S. Pat. No. 5,743,856 includes an electrocardiograph for detecting an electrocardiographic waveform (electrocardiogram), a pressure sensor for detecting a brachial pulse wave occurring to an inflatable cuff, and calculates, as a pulse-wave propagation time, a time difference between a time of detection of an R-wave of the electrocardiogram and a time of detection of a peak of the brachial pulse wave. In addition, the disclosed apparatus calculates a pulse wave propagation velocity by dividing, by the thus calculated pulse wave propagation time, a distance between the heart of the subject and an upper arm on which the cuff is worn.
Based on whether the thus obtained pulse-wave-propagation-velocity-related information is abnormal, it is judged whether a medical treatment, such as administration of drug, is needed.
However, if the obtained pulse-wave-propagation-velocity-related information is a value in the vicinity of a boundary between a normal range and an abnormal range, a correct judgment may not be made to administer drug, based on the pulse-wave-propagation-velocity-related information only.
Recently, it has been elucidated that there are cases where patients suffer arteriosclerosis though their pulse-wave-propagation-velocity-related information is normal and there are cases where subjects do not suffer arteriosclerosis though their pulse-wave-propagation-velocity-related information is abnormal. More specifically described, pulse-wave-propagation-velocity-related information changes with not only arteriosclerosis degree but also blood pressure. Therefore, in the case where subject""s blood pressure is lowered by use of antihypertensive drug, the subject shows normal pulse-wave-propagation-velocity-related information, even if the subject may suffer arteriosclerosis. In addition, in the case where a subject suffers hypertension, the subject shows abnormal pulse-wave-propagation-velocity-related information, even though the subject may not suffer arteriosclerosis.
Meanwhile, an augmentation index, AI, is known as an index for evaluating a degree of arteriosclerosis. Generally, this index is calculated as a percentage of an augmentation between a magnitude of a peak of a pulse wave and a magnitude of a peak of an incident-wave component contained in the pulse wave, relative to a pulse pressure of the pulse wave. However, since a correlation of the augmentation index with respect to arteriosclerosis is lower than that of the pulse-wave-propagation-velocity-related information, the reliability of a diagnosis made based on the augmentation index only is low.
It is therefore an object of the present invention to provide an arteriosclerosis evaluating apparatus for evaluating a degree of arteriosclerosis of a living subject with high accuracy.
The above object has been achieved by the present invention. According to a first aspect of the present invention, there is provided an apparatus for evaluating a degree of arteriosclerosis of a living subject, comprising a pulse-wave-propagation-velocity-related-information obtaining device which obtains pulse-wave-propagation-velocity-related information that is related to a velocity at which a pulse wave propagates in the subject; a pulse-wave sensor which is adapted to be worn on a body portion of the subject and detects the pulse wave from the body portion; an augmentation-related-information obtaining means for obtaining augmentation-related information that is related to an augmentation of an amplitude of the pulse wave detected by the pulse-wave sensor from an amplitude of an incident-wave component which is contained in the pulse wave; and an arteriosclerosis evaluating means for evaluating the degree of arteriosclerosis of the subject, based on the pulse-wave-propagation-velocity-related information obtained by the pulse-wave-propagation-velocity-related-information obtaining device and the augmentation-related information obtained by the augmentation-related-information obtaining means, according to a prescribed relationship between (A) (a1) pulse-wave-propagation-velocity-related information and (a2) augmentation-elated information and (B) degree of arteriosclerosis.
According to this invention, the arteriosclerosis evaluating means evaluates the degree of arteriosclerosis, based on two sorts of information, i.e., the pulse-wave-propagation-velocity-related information obtained by the pulse-wave-propagation-velocity-related-information obtaining device and the augmentation-related information obtained by the augmentation-related-information obtaining means. Therefore, the present apparatus enjoys improved accuracy of the arteriosclerosis evaluation.
According to a second aspect of the present invention, there is provided an apparatus for evaluation of a degree of arteriosclerosis of a living subject, comprising a pulse-wave-propagation-velocity-related-information obtaining device which obtains pulse-wave-propagation-velocity-related information that is related to a velocity at which a pulse wave propagates in the subject; a pulse-wave sensor which is adapted to be worn on a body portion of the subject and detects the pulse wave from the body portion; an augmentation-related-information obtaining means for obtaining augmentation-related information that is related to an augmentation of an amplitude of the pulse wave detected by the pulse-wave sensor from an amplitude of an incident-wave component which is contained in the pulse wave; and a simultaneously displaying device which simultaneously displays the pulse-wave-propagation-velocity-related information obtained by the pulse-wave-propagation-velocity-related-information obtaining device and the augmentation-related information obtained by the augmentation-related-information obtaining means.
According to this invention, the simultaneously displaying device simultaneously displays the pulse-wave-propagation-velocity-related information and the augmentation-related information each of which reflects a degree of arteriosclerosis. Therefore, a medical person can make, based on the pulse-wave-propagation-velocity-related information and the augmentation-related information, a more accurate diagnosis about the degree of arteriosclerosis, than a diagnosis made based on the pulse-wave-propagation-velocity-related information only. For example, in the case where the medical person cannot make a clear judgment about whether there is a need to treat a patient, e.g., administer drug, based on the pulse-wave-propagation-velocity-related information only, the person can judge that the treatment is needed, if the augmentation-related information indicates that the patient suffers arteriosclerosis.
Preferably, the augmentation-related-information obtaining device comprises augmentation-index determining means for determining, as the augmentation-related information, an augmentation index indicative of the augmentation of the amplitude of the pulse wave from the amplitude of the incident-wave component, and the simultaneously displaying device comprises a display device which displays, in a two-dimensional coordinate system defined by a first axis representative of pulse-wave-propagation-velocity-related information and a second axis representative of augmentation index, a symbol at a position having a pair of coordinates corresponding to the pulse-wave-propagation-velocity-related information obtained by the pulse-wave-propagation-velocity-related-information obtaining device and the augmentation index determined by the augmentation-index determining means. According to this feature, the medical person can easily make, based on the position of the symbol displayed in the two-dimensional coordinate system, a diagnosis about the degree of arteriosclerosis.
Preferably, the display device displays the two-dimensional coordinate system which includes an arteriosclerosis area corresponding to an arteriosclerosis range of each of the pulse-wave-propagation-velocity-related information and the augmentation index represented by the first and second axes, and al least one of an arteriosclerosis-suspect area corresponding to a normal range of the pulse-wave-propagation-velocity-related information and the arteriosclerosis range of the augmentation index and a hypertension area corresponding to the arteriosclerosis range of the pulse-wave-propagation-velocity-related information and a normal range of the augmentation index. According to this feature, if the symbol is displayed in the arteriosclerosis area, the medical person can easily evaluate the degree of arteriosclerosis. If the symbol is displayed in the arteriosclerosis-suspect area, the person can speculate that the subject is highly suspected of arteriosclerosis and the subject""s blood pressure is kept low by use of antihypertensive drug; and if the symbol is displayed in the hypertension area, the person can speculate that the subject is not suspected of arteriosclerosis but the subject suffers hypertension and that the subject would probably suffer arteriosclerosis in future.
Preferably, the pulse-wave-propagation-velocity-related-information obtaining device comprises an incident-wave-peak determining means for determining a peak of the incident-wave component contained in the pulse wave detected by the pulse-wave sensor; a reflected-wave-peak determining means for determining a peak of a reflected-wave component which is contained in the pulse wave detected by the pulse-wave sensor; and an obtaining means for obtaining the pulse-wave-propagation-velocity-related information based on the peak of the incident-wave component determined by the incident-wave-peak determining means and the peak of the reflected-wave component determined by the reflected-wave-peak determining means.
According to this feature, the incident-wave-peak determining means determines the peak of the incident-wave component of the pulse wave detected by the pulse-wave sensor, the reflected-wave-peak determining means determines the peak of the reflected-wave component of the pulse wave, and the obtaining means obtains the pulse-wave-propagation-velocity-related information based, e.g., a time difference between the peak of the incident-wave component and the peak of the reflected-wave component. In the case where the augmentation index is determined based on the pulse wave detected by the pulse-wave sensor, the present apparatus can obtain both the pulse-wave-propagation-velocity-related information and the augmentation index, by employing the single pulse-wave sensor.